1. Field of the Invention
The present invention relates to a method of adjusting a recording head of a helical scan system magnetic tape recording and reproducing apparatus and a magnetic tape recording and reproducing apparatus in which magnetic heads can be easily calibrated by users
2. Description of the Related Art
In general, in a helical scan system magnetic tape recording and reproducing apparatus, reproducing heads of the same number as n recording heads, for example, are mounted on a rotary drum. Then, as shown in FIG. 1, a rotary axis of the rotary drum is located in the direction oblique to the running direction of a magnetic tape so that a magnetic tape is helically (spirally) wound around the rotary drum of the magnetic tape recording and reproducing apparatus. In consequence, the magnetic tape is transported at a constant velocity at the same time heads on the rotary drum are rotated and thereby the heads are able to scan the magnetic tape helically (that is, in a helical scan fashion).
More specifically, as shown in FIG. 2, in a magnetic tape recording and reproducing apparatus including a rotary drum 20 onto which two recording heads HW1, HW2 and two reproducing heads HR1, HR2 are attached at an interval of 90 degrees relative to the rotation center of the rotary drum 20, a magnetic tape (hereinafter simply referred to as a “tape”) 10 is wrapped around the rotary drum 10. The tape 10 is transported at a constant velocity at the same time the rotary drum 20 starts to rotate. As a result, the recording heads HW1, HW2 and the reproducing HR1, HR2 become able to scan the tape 10 helically (see FIG. 1).
Then, when magnetic information is recorded on the tape 10 by the two recording heads HW1 and HW2, as shown in FIG. 3, belt-like tracks Tr, . . . , in which magnetic information is recorded (written) are obliquely formed on the tape 10. It should be noted that, in FIG. 3, Tr1 represents a track formed on the tape 10 by the recording head HW1 and that Tr2 represents a track formed on the tape 10 by the recording head HW2.
Also, when the tape 10 in which the tracks Tr1 and the tracks Tr2 are formed is reproduced by the two reproducing heads HR1 and HR2, magnetic information recorded on the track Tr1 is reproduced by the reproducing head HR1 and magnetic information recorded on the track Tr2 is reproduced by the reproducing head HR2, respectively.
As described above, in the magnetic tape recording and reproducing apparatus including the two recording heads HW1, HW2 and the two reproducing heads HR1, HR2 shown in FIG. 2, it is customary that magnetic information recorded by the recording head HW1 is reproduced by the reproducing head HR1, magnetic information recorded by the recording head HW2 is reproduced by the reproducing head HR2 and that the tracks Tr1 and Tr2 makes a pair.
More specifically, in the magnetic tape recording and reproducing apparatus in which n recording heads HWi (i=1 to n) and reproducing heads HRi (i=1 to n) of the same number as that of the recording heads HWi are mounted on the rotary drum, the recording heads HWi and the reproducing heads HRi may correspond to each other in a one-to-one correspondence fashion and n tracks may form a set of tracks.
Then, according to the head arrangement shown in FIG. 2, in the normal operation state in which the tape 10 is transported at a normal tape transport speed of a predetermined value and in which the rotary drum 20 is rotated at a normal rotating speed of a predetermined value under control, the recording head HW1 and the reproducing head HR1 may scan the area of the track Tr1 shown in FIG. 3 during 0.5 rotation of the first half of one rotation of the rotary drum 20 and the recording head HW2 and the reproducing head HR2 may scan the area of the track Tr2 shown in FIG. 3 during 0.5 rotation of the second half of one rotation of the rotary drum 20. Finally, the two tracks Tr1 and Tr2 are scanned substantially simultaneously by the heads during one rotation of the rotary drum 20.
In recent years, needs of high density recording are extremely increased in order to record much more information on a magnetic tape. Concurrently therewith, there is a tendency that a width of a track in which magnetic information is recorded should be progressively decreased more than ever. Examples of track widths will be described. In the AIT4 tape format that is now commercially available, a track width is 4.4 μm and a magnetic tape recording and reproducing system corresponding to a narrower track width of 2 to 3 μm is now under examination.
A problem that encounters with introduction of a magnetic tape recording and reproducing system for recording and reproducing a magnetic tape having such a narrow track width is dispersions of heights with which a plurality of recording heads HW may be attached to the head attachment surface of the rotary drum 20.
More specifically, when the tape is originally transported at a predetermined tape transport speed, if the two recording heads HW1 and HW2 are attached to the proper positions of the rotary drum 20 having the head arrangement shown in FIG. 2, then widths of the magnetic patterns recorded on the track Tr1 and Tr2 are formed at an equal interval as shown in FIG. 3. However, if the recording heads HW1 and HW2 are different in height and they are not attached to the proper positions of the rotary drum 20, then the widths of magnetic patterns recorded on the tracks Tr1 and Tr2 are not formed at an equal interval, that is, the narrow tracks Tr1 and the wide tracks Tr2 are formed alternately as shown in FIG. 4, for example. For this reason, there is a risk that errors will be frequently detected from the narrow tracks Tr1 by an error detection process executed upon reproduction.
In order to cope with such situations, according to the related-art, a reproducing head is attached to an actuator formed of a suitable device such as a bimorph piezoelectric element and a moving coil and the height of the reproducing head is controlled by the actuator such that a reproduced signal may become an excellent reproduced signal obtained when information recorded on the tracks of the magnetic tape is reproduced by the reproducing head. However, in the magnetic tape recording and reproducing apparatus including the head driving mechanism with the actuator according to the related art, it has been customary that only the reproducing head is driven under control of the actuator while the recording head is separately fixed to the rotary drum without using the actuator.
More specifically, when the recording head HW is attached to and fixed to the rotary drum, it is customary to adjust the height of the recording head HW relative to the head attachment surface of the rotary drum. This height adjusting method will be described with reference to FIG. 5. As shown in FIG. 5, the other end side of a head attachment metal part 27 provided at one end of the recording head HW is fixed to the predetermined position of the rotary drum 20 by a head base fixing screw 28 in a cantilever fashion. Further, the height of the recording head HW may be adjusted by deforming the head attachment metal part 27 with a head height adjusting screw 29.
As described above, according to the related art, while the actuator is not provided on the recording head HW, the actuator is provided on the reproducing head HR. The reason for this will be described below. In the reproducing operation, even though tracks have substantially the same angles of inclination (azimuth angles), it becomes more difficult to stably obtain a reproduced signal as the width of the track is decreased more, and inclinations of angle of the tracks may not be negligible. Hence, it is necessary that the reproducing head should be controlled so as to follow the inclinations of angle of the tracks. For this reason, in the reproducing operation, the magnetic tape is reproduced by the reproducing head HR while the reproducing head HR is being displaced under control of dynamic tracking servo so that read errors generated at that time can be improved.
On the other hand, in the recording operation, even though information was already recorded on the tracks of the tape, since new information is overwritten on the tracks by the recording head and thereby new tracks are formed, it is not necessary to positively drive the recording head by the actuator and it is sufficient that the recording head should be fixed to the predetermined position of the rotary drum through adjustment.
Also, concerning the height adjustment of the recording head of the helical scan system magnetic tape recording and reproducing apparatus, there have hitherto been known technologies disclosed in Cited Patent Reference 1 and Cited Patent Reference 2.
First, the Cited Patent Reference 1 discloses a rotary drum apparatus that can be applied to a magnetic recording and reproducing apparatus such as a data recorder and a video tape recorder.
The rotary drum apparatus described in this Cited Patent Reference 1 includes a magnetic head height detecting device (displacement sensor) to measure a height of a magnetic head serving as a recording and reproducing magnetic head to thereby output measured results of height, a magnetic head height varying device (piezoelectric element and actuator) capable of varying the height of the magnetic head within a range of substantially one track pitch in response to a drive signal with respect to the rotary axis direction of the rotary drum and a driving unit for outputting a drive signal based on the height measured results obtained by the height detecting device. Then, particularly, in the final adjustment process, relative positional data obtained from the magnetic heads by using a predetermined reference tape is stored in a memory circuit, a relative height of the magnetic head is monitored and this relative height is held at a predetermined value based on the relative positional data stored in the memory circuit, thereby resulting in the height of the magnetic head mounted on the rotary drum being adjusted.
Also, the Cited Patent Reference 1 discloses a rotary drum apparatus for use with a helical scan system magnetic tape recording and reproducing apparatus and which includes a pair of piezoelectric bimorphs (actuators) symmetrically attached thereto around the axis of a rotary drum and more than one set of a pair of a set of recording and reproducing heads, each having an inverse azimuth angle relative to the pair of piezoelectric bimorphs, mounted along the outer peripheral surface of the rotary drum. Then, when magnetic information is recorded on the magnetic tape, this rotary drum apparatus may adjust the height of the other recording and reproducing head so as to agree with the reference height with references the head height of one recording and reproducing head of a pair of recording and reproducing heads.
More specifically, as shown in FIG. 6A, the magnetic tape recording and reproducing apparatus described in the Cited Patent Reference 2 may use the rotary drum 20 having the head arrangement shown in FIG. 2 and it may form a track Tr1 with one azimuth angle by the recording head HW1 and a track Tr2 with the other azimuth angle by the recording head HW2 substantially at the same time at tape transport speed of zero when the rotary drum is rotated once. Then, having started from this state, the magnetic tape recording and reproducing apparatus rotates the rotary drum 20 a plurality of times to cause the recording head HW1 to scan the track Tr2 in the direction shown by an arrow a in FIG. 6B and thus the track Tr2 is overwritten a plurality of times by the track Tr1. At that time, as shown in FIG. 6B, the height of the recording head HW1 is progressively changed by the actuator such that a width a may be decreased. Then, when only the reproduced signal of the track Tr1 with one azimuth angle is detected, it may be determined the two recording heads HW1 and HW2 are located at the proper positions.
[Cited Patent Reference 1]: Japanese Published Patent Application No. Hei 8-63730 (page 2, FIG. 1)
[Cited Patent Reference 2]: Japanese Published Patent Application No. 2001-184616 (page 2, FIGS. 1 and 16)